Nitrile rubbers represented by an acrylonitrile-butadiene copolymer rubber (hereinafter referred to as "NBR" when appropriate) have heretofore been used for fuel hoses for automobiles. Recently importance is placed on the resistance of fuel hoses to sour-gasoline and alcohol-mixed gasoline. A mixture of NBR with polyvinyl chloride (hereinafter referred to as "polyblend" when appropriate) is used as a rubber material for an inlet filler hose for which a good sour-gasoline resistance is required, and fluororubber is used as a rubber material for an inlet filler hose for which a good alcohol-mixed gasoline resistance is required.
Fluororubber has good thermal resistance, oil resistance, solvent resistance and chemical resistance, but is relatively expensive as compared with other rubbers and has a poor cold resistance. To cope with the deficiency of fluororubber, attention is attracted to a rubber laminate comprising a fluororubber composition layer and another rubber composition layer.
A laminate of a fluororubber composition layer and a nitrile rubber composition layer, made by a conventional laminating procedure, has a problem such that the adhesion between the two rubber composition layers is poor. To enhance the adhesion, various proposals have heretofore been made. For example, a method has been proposed wherein a fluororubber composition layer having incorporated therein a polyol vulcanizer and a metal oxide is adhered to a nitrile rubber composition layer having incorporated therein a sulfur-containing vulcanizer and tetrabutylphosphonium benzotriazolate, which is a special salt made from an organic phosphonium compound and a benzotriazolate compound (Japanese Unexamined Patent Publication No. 63-252736). This method has a problem such that the nitrile rubber composition layer containing a sulfur-containing vulcanizer tends to scorch during processing operation, i.e., the rubber composition is subject to a premature cure during processing operation before the vulcanization step, and consequently vulcanization and other operations become . difficult.
To solve the scorch problem, a proposal of incorporating an organic peroxide crosslinking system and a sulfenamide compound into the nitrile rubber composition layer containing tetrabutylphosphonium benzotriazolate has been made (Japanese Unexamined Patent Publication No. 1-110141). The problem of scorch can be solved by this proposal, but, to enhance the adhesion between the fluororubber composition layer and the nitrile rubber composition layer, a salient amount of calcium hydroxide must be incorporated in the nitrile rubber composition layer, with the results that thermal aging resistance of the fluororubber/nitrile rubber laminate is reduced and an adverse influence is exerted on the balanced properties including a permanent set of the vulcanized product.